Radiation therapy is a common technique for treating cancer or reducing the likelihood of re-occurrence of cancer by using high-energy radiation to kill cancer cells and to shrink or eliminate tumors. In a planning phase, images of a portion of a patient's body are acquired or generated (e.g., showing the location of a tumor and surrounding normal areas), and a treatment plan is developed based on the images. For example, a radiation oncologist may determine the area of the patient's body to be treated with radiation, the amount of radiation dose to be delivered, and geometrical details (e.g., angles or trajectories) of the dose delivery. Subsequently, in a treatment phase, radiation is delivered to the patient's body in accordance with the treatment plan.
In some known radiation therapy treatment systems, a movable gantry is used to deliver a radiation dose to a patient lying in a patient couch (also referred to as a bed, a support, or a table). The gantry includes a beam generator or a treatment head configured to generate an electron (particle) beam or an x-ray (photon) beam to be delivered to the patient. Other devices, such as imaging devices, may be attached to the gantry, and these devices and the gantry are collectively referred to as a treatment machine. The treatment machine and the couch are often independently movable to various orientations, wherein the independent motion capabilities of the treatment machine and of the couch enable various radiation treatment plans to be implemented. However, those motion capabilities exacerbate one of the main risks of radiation therapy treatment: the risk of collision between the treatment machine and the patient. In general, with a large, heavy piece of equipment moving near the patient, there is the risk that the patient may move part of the patient's body and cause a collision, possibly endangering the patient and/or causing damage to equipment. This risk is increased when there are at least two independently moving elements (the couch and the treatment machine) and the patient might also move in an unexpected way. One approach for addressing this collision risk has been be to take a conservative approach in treatment planning regarding motion of, e.g., the couch. For example, couch rotations might not be permitted in the treatment plan, or only relatively small amounts of couch rotation might be permitted. However, various complex treatments, such as stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT), involve relatively steep radiation dose gradients, which emphasizes the role of precise dose delivery, accurate positioning and imaging of the patient's body, and, in turn, demanding increased range of possible motions.
Consequently, the machine-to-patient clearance margin is reduced in many treatment scenarios, particularly when the imaging system introduces an additional collision risk factor. For example, imaging devices attached to the gantry may be in a retracted state or a deployed state at various orientations and times during the radiation treatment, and the imaging devices might collide with the patient. Additionally, the treatment machine might collide with any of various setup aids (e.g., arm rests, breast boards, etc.) or other equipment associated with radiation treatment (e.g., a visual coaching device, mounted to the couch in front of the patient's face, that provides respiratory coaching to the patient). For convenience, these various setup aids and other equipment associated with radiation treatment may be referred to as assistive devices. A collision between the treatment machine and any assistive device is undesirable as well.